Depression of sulfide minerals with zinc cyanide ammoniate



Patented Nov. 24, 1953 DEPRESSION F SULF IDE MINERALS WITH ZINC CYANIDE AItIlVlONIA'IE Charles Francis Allen, Stamford, Conn., Worth Martin Fitzsimmons, Sacramento, Calif., and Robert Ben Booth, Stamford, Conn., assignors to American Cyanamid Company, New York, N. Y., a corporation of Maine No Drawing. Application September 5, 1952, Serial No. 308,156

This invention relates to an improved process of froth flotation of ores containing sulfides of both copper and zinc.

In the past, cyanides have been used to depress zinc sulfides in the frot'i flotation of ores containing zinc and lead sulfides, copper and zinc sulfides, or zinc, lead and copper sulfides. These cyanides were usually of the alkali or alkalineearth metals. One of the most commonly used is crude calcium cyanide, obtained by an electric furnace process from calcium cyanamid and carbon, and sold by the American Cyanamid Company under the name of Aero Brand Cyanide, commonly referred to in the trade by its trade marked name.

In the application of Allen and Booth, Serial No. 242,184, new Patent No. 2,620,063, filed August 16, 1951, there is described and claimed a process of depressing copper sulfides using a zinc cyanide ammonia complex which may be obtained by reacting zinc cyanide with ammonia and which will hereinafter be referred to as a1nmoniated zinc cyanide. This product, as de scribed and claimed in the above application, was capable of depressing copper sulfides, which hitherto, were not affected materially by cyanides. The amount of the ammoniated zinc cyanide used was normally. considerably in excess of 2 lb./ton of ore feed treated in the froth flotation process.

According to the present invention, we have found that if smaller amounts of ammoniated zinc cyanide, ranging from to 2%, lb./ton of feed, the result is just the opposite: instead of depressing the copper sulfides, they float readily,

but zinc sulfides and iron sulfides are very eifi-- ciently depressed. It is not known why the zinc' cyanide ammonia complexes exhibit this sharp change in effect when used with the same ore under the same flotation conditions but-in differ ent amounts. It is not intended to limit the present invention to any theory as to why the ammoniated zinc cyanide behaves so differently in large amounts than it does in smaller amounts.

Not only is the behavior of the ammoniated zinc cyanide very different in the range used in the present invention, but in its depression of sulfides of zinc and iron it is far more efficient than cyanides of the alkali and alkaline-earth metals. Again, it is not known why this additional efiiciency is obtained, because in the ordinary use of alkali or alkaline-earth metal cyanides, there is presentzinc sulfate, and so there must be formation of zinc cyanide to a considerable extent. It is not, therefore, a question of using a zinc cyanide in place'oi an alkali or alkaline-earth metal cyanide, but rather the marked improvement which results when ammoniated zinc cyanide is used.

It is a further advantage of the present inven tion that the marked increase in depression efficiency of the ammoniated zinc cyanide is not off- 8 Claims. (Cl. 209-167) set by a loss in grade of lead and lead-copper and copper concentrate; nor are the recoveries of these minerals materially reduced and, in some cases, particularly in the case of copper, the recoveries may actually increased. This is a rather unusual result in froth flotation, because ordinarily grade and recovery represents a com.

promise; and flotation reagents or flotation conditions which make for very intense flotation will favor recovery but reduce grade, and vice versa. This compromise has been an unfortunate characteristic of most froth flotation processes and the present invention represents a rather unusual situation, where an improved selectivity, as represented by greater depression of the zinc sulfide and iron sulfide minerals, is effected with out loss of recovery of the desired copper minerals and, in some cases, with actual increase in recovery. Why the ordinary compromise which is noted in froth flotation operations does not apply in the present case is not known, and here again no theory is advanced for the usual behavior of the ammoniated zinc cyanide.

In the present invention, the ammonia must be present in the form of a complex salt and not joined to the other components of the complex by ordinary stable chemical ionic valent linkages. Thus, for example, ammonium zinc cyanide which is a definite chemical compound does not show the high effectiveness of the ammoniated zinc cyanide of the present invention, even though the three constituents of the ammoniated zinc cyanide, i. e., ammonia, zinc and the cyanide radical, are all present in the same chemical compound. It is not known why the effectiveness of the present invention is obtained only when a complex of ammonia and cyanide is present, nor is it known why the salt-like chemical union of ammonia with cyanide to form a compound linked by ordinary ionic valence linkages defeats the improved depressing action. No theory. is advanced as to why the complex works well, whereas when the same constituents are ionically bound, the improved results are not attained. Accordingly, the invention is not limited to any theory as to why the peculiar chemical constitution of the depressant operates.

It is an advantage of the present invention that the method by which the ammoniated zinc cyanide complex is produced is not critical. This may be effected by various means; for example, zinc salt, cyanide and ammonium hydroxide may be reacted together to produce the complex. Another method involves the reaction of gaseous ammonia with a zinc salt, which is then reacted with an ordinary cyanide. A third method involves ammoniating. the cyanide and mixing it with a Zinc salt; and finally, a fourth method, which is the cheapest and preferred, as it produces, the most active complex, involves ammoniating preformed zinocyanide.

The proportions of the ingredients going into the complex are not critical. It is desirable to operate with equimolal amounts of the metals and cyanide. The amount of ammonia, however, in its basic form may vary quite widely and may be determined by the amount of ammonia which the metal salt or the zinc cvanide will absorb.

The present invention may be used with ores in rougher flotation operations, or it may be used to treat concentrates. It is an advantage of the present invention that when precious metals are present, associated with sulfides, for example, when there is present auriferrous pyrite, the ammoniated zinc cyanide does not tend to dissolve out the gold, which is concentrated with the pyrite and can be recovered from the rougher tailing by conventional means. Here again it is not known why there is no serious dissolution of precious metal. It seems probable that this may be tied up with the difierent chemical nature of the ammonium complex, in which the linkage is not ionic. However, other factors may be present and here again it is not desired to limit the invention to a particular theory.

As far as the froth flotation operation itself is concerned, the present invention does not de part from the normal procedure. This is an advantage, as no new techniques or critical operations are required. Ordinary sulfide promoters are used in the customary amounts which normally operate well with a particular ore. The flotation proceeds smoothly and the advantages of the present invention are therefore obtained without any offsetting disadvantages in operating conditions.

The invention will be described in greater detail in conjunction with the specific examples, the parts being by weight unless otherwise specified.

EXAMPLE 1 A sample of South West Africa lead-copperzinc ore was ground with 3.0 pounds per ton of soda ash, 0.50 pound per ton of sodium cyanide and 1.8 pounds per ton of zinc sulfate. The ground pulp was conditioned for 1 minute with 0.10 pound per ton of potassium ethyl xanthate and 0.06 pound per ton of an alcohol type frother. A lead-copper concentrate was then removed by flotation for a period of 3 minutes. During the flotation period 0.02 pound of potassium ethyl xanthate and 0.10 pound per ton of alcohol frother were added. The rougher lead-copper concentrate assayed 40.0% Pb, 10.6% Cu and 7.8% Zn, recovering 96.2% of the lead, 86.2% of the copper and 40.5% of the zinc. The lead and copper recoveries in this product corresponded closely to results obtained in practice. The recovery of zinc in the lead-copper concentrate is generally about 30% in mill operation. It was found that if 1.25 pounds per ton of zinc cyanide ammoniate was substituted for sodium cyanide and zinc sulfate, the results improved materially in that approximately 4% more copper was recovered in the lead-copper concentrate and 18% more zinc was rejected from this product. The

third test was run in which the soda ash was deleted. This resulted in an additional recovery of 2.2% more copper in the flotation concentrate and the rejection of an additional 4.9% of the zinc from the lead-copper concentrate. The metallurgical results obtained in these three tests are given in Table I.

It will be noted that there is a very slight loss in lead recovery when the zinc cyanide ammoniate is used, amounting in one test to somewhat over 3%. This does not indicate a depression of lead by the zinc cyanide ammoniate. On the contrary, it is recognized that in the ore used, a looking exists between galena and sphalerite and so the slight loss in lead recovery is no doubt due to the fact that some lead is lost in middlings, which contain both sphaierite and galena. Losses of lead are very small, compared to the great increase in depression efficiency and, in the case of copper, there is an actual increase in recovery, from 86-92%. The amounts of zinc cyanide ammoniate and sodium cyanide used in the various tests represent approximately optimum amounts of each reagent for the particular ore in question.

EXAMPLE 2 On a sample of South American lead-copperzinc ore assaying approximately 2.7% Pb, 3.4%

Cu, 3.9% Zn and 22.0% Fe was ground with 5.0 pounds per ton of hydrated lime, 2.5 pounds per ton of Aero Brand Cyanide and 2.25 pounds per ton of zinc sulfate. The ground pulp was conditioned for 1 minute with 0.10 pound per ton of sodium butyl Xanthate and 0.09 pound per ton of pine oil. A lead-copper concentrate was removed by flotation for a period of 9 minutes. During the flotation period 0.05 pound per ton of sodium butyl xanthate and 0.06 pound per ton of pine oil were added. A comparative test was run to this test in which 2.25 pounds per ton of zinc cyanide ammoniate was substituted for the combination of Aero Brand Cyanide and zinc sulfate. The recovery of lead in these two tests was almost identical. In the test using Aero Brand Cyanide and zinc sulfate 78.6% of the copper and 43.2% of the zinc were recovered in the lead-copper concentrate, In the test using zinc cyanide ammoniate 76.1% of the copper and 30.1% of the zinc were recovered in the lead-copper concentrate. Metallurgical results obtained in these two tests are given in Table II.

Table II Reagent variables Bougher Pb-Cu concentrate Assay Distribution Pb Cu Zn Fe Pb Cu Zn Fe Zinc Aero brand Zinc cyanide cyanide sulfate an momate moo coco

It will be noted that in this example the amount of zinc cyanide ammoniate slightly exceeds the minimum amount which has been described in application 242,184 for the depression of copper. As was pointed out there, the range is a practical one, and in common with most froth fiotation operations, the amounts of reagents will vary somewhat from one ore to another. In the case of the ore of Example 2, the amount of zinc cyanide ammoniate used is far too little to depress copper, this being an ore which requires a considerably larger amount of ammoniated zinc cyanide than the minimum specified in the application of Allen and Booth referred to above.

EXAMPLE 3 A Spanish. pyrite ore containing approximately 2.4% Cu and 2.0% Zn was ground with 5.0 pounds per ton of hydrated lime, 1.25 pounds per ton of Aero Brand Cyanide and 2.8 pounds per ton of Zinc sulfate. A copper concentrate was then removed by flotation with 0.10 pound per ton of sodium isoprop-yl xanthate and 0.09 pound per ton of pine oil. A comparative test was run in which 1.33 pounds per ton of zinc cyanide ammoniate Was substituted for the combination of Aero Brand Cyanide and zinc sulfate. In the test using Aero Brand Cyanide and zinc sulfate 79.1% of the copper and 15.0% of the zinc was recovered in the copper concentrate. In the test in which zinc cyanide ammoniate was used 823% of the copper and 14.4% of the zinc was recovered in the copper concentrate. The metallurgical results in these tests are given in Table III.

A sample of low grade Canadian copper-zinc ore assaying 0.94% Cu and 3.6% Zn was ground with 1.5 pounds per ton of hydrated lime and 1.7 pounds per ton of zinc cyanide ammoniate. The ground pulp was conditioned for 1 minute with 0.07 pound per ton of a mixture of the sodium salts of mercaptobenzothiazole and (ii-secondary bu'tyl dithiophosphate and 0.06 pound per ton of a six-carbon alcohol type frother. A copper concentrate was then floated which recovered 93.1% of the copper and 30.0 of the zinc into a rougher concentrate assaying 10.7% Cu and 13.3% Zn.

We claim:

1. A process of selectively depressing sulfides of zinc and iron in the presence of sulfides of copper which comprises effecting froth flotation in the presence of an effective amount of a collector for copper sulfides and an ammonia zinc cyanide complex as a depressant, the ammonia being linked non-ironically, the amount of depressant being not less than lb./ton of flotation feed and insufiicient to substantially depress the flotation of copper sulfides.

2. A process according to claim 1 in which the depressant. is an amznoniated zinc cyanide obo tained by reacting zinc cyanide with gaseous ammonia.

3. A process according to claim 2 in which the ore contains zinc sulfides but is substantially free from iron sulfides.

4. A process according to claim 1 in which the ore contains zinc sulfides but is substantially free from iron sulfides.

5. A process according to claim 1 in which the ore contains both sulfides of zinc and iron.

6. A process according to claim 5 in which the iron sulfide is auriferrous pyrite.

7. A process according to claim 6 in which the depressant is prepared by treating zinc cyanide with gaseous ammonia.

8. A process according to claim 1 in which the ore contains both sulfides of zinc and sulfides of iron and the depressant is prepared by reacting zinc cyanide with gaseous ammonia.

CHARLES FRANCIS ALLEN. WORTH MARTIN FITZSIMMON S. ROBERT BEN BOOTH.

No references cited. 

1. A PROCESS OF SELECTIVELY DEPRESSING SULFIDES OF ZINC AND IRON IN THE PRESENCE OF SULFIDES OF COPPER WHICH COMPRISES EFFECTING FROTH FLOTATION IN THE PRESENCE OF AN EFFECTIVE AMOUNT OF COLLECTOR FOR COPPER SULFIDES AND AN AMMONIA ZINC CYANIDE COMPLEX AS A DEPRESSANT, THE AMMONIA BEING LINKED NON-IRONICALLY THE AMOUNT OF DEPRESSANT BEING NOT LESS THAN 1/4 LB./TON OF FLOTATION FEED AND INSUFFICIENT TO SUBSTANTIALLY DEPRESS THE FLOATTION OF COPPER SULFIDES. 